Drill bit apparatus adapted for use with a dual tube reverse circulation drill string.
In U.S. Re Pat. No. 27,316 to Elenburg there is disclosed a drill bit for a dual pipe reverse circulation system to greatly restrict radial outward flow. The drill bit housing has a depending tubular skirt with cone mounting extensions extending radially inwardly thereof. Radial inner housing extensions extend slightly inwardly of the axial outer portions of the cutters. A nozzle opens on each angular side of each cone mounting extension to discharge fluid inwardly adjacent to and radially inwardly of the skirt to cause cuttings to flow outwardly through the bit central opening. U.S. Pat. No. 3,439,757 to Elenburg discloses another reverse circulation bit that includes a radial outer skirt and weirs extending between the cutter cone shanks with fluid flowing inwardly between the shanks, skirt and and weir and thence radially inwardly to the bit housing central opening.
U.S. Pat. No. 3,685,601 to Hollingshead discloses a non-reverse circulation bit that has passages for discharging fluid downwardly between the exterior surfaces of rotary cutters and a check valve in each passage to prevent fluid returning into the interior of the bit. The bit also has cooling passages for conducting fluid between the pintles and cutters. U.S.S.R. Patent No. 185,300 discloses a roller bit having scavenging channels and a diaphragm with one or more ball check valves in the upper recess above the channels to obstruct entry of cuttings passing into the channels through the clearance space between the leg deflectors and cutters after air feed is stopped.
U.S. Pat. No. 1,874,070 to Wellensieh discloses a collar bit having a plurality of cutter mounting arms secured to an annular cutter head to extend thereabove and radially outwardly thereof in angularly spaced relationship while U.S. Pat. No. 3,292,719 to Schumacher, Jr. discloses cutter assemblies welded to the lower surface of a bit head with the cutters, for the most part, located in the annular space radially between the outer and central skirts. Fluid is forced inwardly exterior of the drill string.
In order to provide an improved reverse circulation bit and permitting drilling deeper bore holes to recover core cuttings in a shorter perior of time this invention has been made.